50+ Basic Operating System Interview Questions & Answers for 2025 Success

Preparing for a technical interview can be nerve-wracking, especially when it comes to operating system concepts. Whether you're a fresh graduate or an experienced developer switching roles, mastering basic operating system interview questions is crucial for landing your dream job in tech.

This comprehensive guide provides you with 50+ carefully curated basic operating system interview questions along with detailed answers. Each question has been selected based on its frequency in real interviews at top tech companies. Let's dive into the questions that could make or break your next interview.

Process Management Interview Questions (Questions 1-15)

1. What is an Operating System?

Answer: An operating system (OS) is system software that manages computer hardware and software resources. It acts as an interface between the user and computer hardware, providing services like process management, memory management, file system management, and device management.

2. What is a Process?

Answer: A process is a program in execution. It includes the program code (text section), current activity represented by the program counter, processor registers, and variables. A process is an active entity, unlike a program, which is passive.

3. What are the different states of a process?

Answer: A process can be in one of five states:

• New: Process is being created

• Ready: The Process is waiting to be assigned to a processor

• Running: Instructions are being executed

• Waiting/Blocked: Process is waiting for some event (I/O completion)

• Terminated: Process has finished execution

4. What is the difference between a process and a program?

Answer:

• Program: Static entity stored on disk, passive, permanent until deleted

• Process: Dynamic entity loaded in memory, active, temporary (exists during execution)

• One program can have multiple processes running simultaneously

5. What is a Process Control Block (PCB)?

Answer: PCB is a data structure containing all information about a process:

• Process ID (PID)

• Process state

• Program counter

• CPU registers

• Memory management information

• I/O status information

• Accounting information

6. What is Context Switching?

Answer: Context switching is the process of saving the current state of a running process and loading the saved state of another process. It involves:

• Saving the current process context in PCB

• Loading next process context from PCB

• Switching CPU control to the new process

7. What is the difference between preemptive and non-preemptive scheduling?

Answer:

• Preemptive: OS can forcibly remove a process from the CPU (e.g., Round Robin)

• Non-preemptive: Process voluntarily releases CPU (e.g., FCFS)

8. What is a Thread?

Answer: A thread is a lightweight subprocess that shares memory space with other threads in the same process. Threads have faster creation time and context switching compared to processes.

9. What is the difference between a process and a thread?

Answer:

• Process: Independent memory space, expensive creation, slower context switching

• Thread: Shared memory space, cheaper creation, faster context switching

10. What is multithreading?

Answer: Multithreading is the ability of an OS to support multiple threads of execution within a single process simultaneously, improving application performance and responsiveness.

11. What are the benefits of multithreading?

Answer:

• Improved responsiveness

• Resource sharing

• Economy (less overhead)

• Scalability on multiprocessor systems

12. What is a zombie process?

Answer: A zombie process is a process that has completed execution but still has an entry in the process table. It occurs when a child process finishes but the parent hasn't called wait() to read its exit status.

13. What is an orphan process?

Answer: An orphan process is a process whose parent has terminated. The init process (PID 1) becomes the parent of orphan processes and eventually cleans them up.

14. What is process synchronization?

Answer: Process synchronization is the coordination of simultaneous processes to ensure they don't interfere with each other when accessing shared resources, preventing race conditions.

15. What is a race condition?

Answer: A race condition occurs when multiple processes access shared data simultaneously, and the final outcome depends on the timing of their execution, leading to unpredictable results.

Memory Management Interview Questions (Questions 16-30)

16. What is memory management?

Answer: Memory management is the process of controlling and coordinating computer memory, assigning portions called blocks to various running programs to optimize system performance.

17. What is virtual memory?

Answer: Virtual memory is a memory management technique that uses hardware and software to allow a computer to compensate for physical memory shortages by temporarily transferring pages of data from RAM to disk storage.

18. What is paging?

Answer: Paging is a memory management technique where memory is divided into fixed-size blocks called pages (in logical memory) and frames (in physical memory). It eliminates external fragmentation.

19. What is segmentation?

Answer: Segmentation divides memory into variable-sized segments based on logical divisions of a program (code, data, stack). Each segment can grow or shrink independently.

20. What is the difference between paging and segmentation?

Answer:

• Paging: Fixed-size blocks, eliminates external fragmentation, may cause internal fragmentation

• Segmentation: Variable-size blocks eliminate internal fragmentation, but may cause external fragmentation

21. What is thrashing?

Answer: Thrashing occurs when a system spends more time swapping pages in and out of memory than executing processes, severely degrading performance due to excessive page faults.

22. What is a page fault?

Answer: A page fault occurs when a program tries to access a page that is not currently in physical memory, causing the OS to load the page from secondary storage.

23. What are the different page replacement algorithms?

Answer:

• FIFO (First In First Out): Replace the oldest page

• LRU (Least Recently Used): Replace the least recently used page

• Optimal: Replace the page that won't be used for the longest time

• Second Chance: Modified FIFO with reference bit

24. What is memory fragmentation?

Answer:

• Internal Fragmentation: Unused space within allocated memory blocks

• External Fragmentation: Free memory is scattered in small, unusable blocks

25. What is demand paging?

Answer: Demand paging loads pages into memory only when they are needed (demanded) rather than loading the entire program at once, reducing memory usage and startup time.

26. What is swapping?

Answer: Swapping is moving entire processes between main memory and secondary storage. When memory is full, inactive processes are swapped out to make room for active ones.

27. What is the difference between a logical and physical address?

Answer:

• Logical Address: Generated by CPU, virtual address seen by the process

• Physical Address: Actual address in main memory where data is stored

28. What is a Memory Management Unit (MMU)?

Answer: MMU is hardware that translates logical addresses to physical addresses. It handles virtual memory management and memory protection.

29. What are the different memory allocation techniques?

Answer:

• First Fit: Allocate the first available block large enough

• Best Fit: Allocate the smallest available block that fits

• Worst Fit: Allocate the largest available block

30. What is copy-on-write?

Answer: Copy-on-write is an optimization technique where pages are shared between processes until one process modifies the page, at which point a private copy is created.

CPU Scheduling Interview Questions (Questions 31-40)

31. What is CPU scheduling?

Answer: CPU scheduling is the process of determining which process gets CPU time and for how long. The scheduler selects processes from the ready queue and allocates the CPU to them.

32. What is First Come First Served (FCFS) scheduling?

Answer: FCFS is a non-preemptive scheduling algorithm where processes are executed in the order they arrive. Simple to implement, but can cause the convoy effect where short processes wait behind long ones.

33. What is Shortest Job First (SJF) scheduling?

Answer: SJF selects the process with the smallest execution time. It minimizes average waiting time but requires knowing process execution times in advance and can cause starvation of long processes.

34. What is Round Robin (RR) scheduling?

Answer: RR is a preemptive scheduling algorithm where each process gets a fixed time quantum. When quantum expires, the process is preempted and placed at the end of the ready queue.

35. What is Priority scheduling?

Answer: Priority scheduling assigns priorities to processes and executes the highest priority process first. It can be preemptive or non-preemptive and may cause starvation of low-priority processes.

36. What is aging in CPU scheduling?

Answer: Aging is a technique to prevent starvation by gradually increasing the priority of processes that have been waiting in the ready queue for a long time.

37. What is the convoy effect?

Answer: Convoy effect occurs in FCFS scheduling when short processes get stuck behind long processes, similar to fast cars stuck behind a slow truck on a single-lane road.

38. What is turnaround time and waiting time?

Answer:

• Turnaround Time: Total time from process submission to completion

• Waiting Time: Total time spent waiting in the ready queue

39. What is response time?

Answer: Response time is the time from when a request is submitted until the first response is produced (not completion time). Important for interactive systems.

40. What is multilevel queue scheduling?

Answer: Multilevel queue scheduling partitions processes into different queues based on properties like priority or process type. Each queue can have its own scheduling algorithm.

Synchronization and Deadlock Questions (Questions 41-50)

41. What is a critical section?

Answer: A critical section is a segment of code where shared resources are accessed. Only one process should execute in its critical section at any given time to prevent race conditions.

42. What is mutual exclusion?

Answer: Mutual exclusion ensures that only one process can access a shared resource at a time. It's implemented using synchronization primitives like mutexes and semaphores.

43. What is a semaphore?

Answer: A semaphore is a synchronization primitive that controls access to resources using a counter. Binary semaphores (mutex) allow 0 or 1, while counting semaphores allow multiple values.

44. What is a mutex?

Answer: A mutex (mutual exclusion) is a binary semaphore used to protect shared resources. Only the thread that locks a mutex can unlock it, providing ownership semantics.

45. What is a deadlock?

Answer: A Deadlock is a situation where processes are blocked indefinitely, each waiting for resources held by others. No process can proceed, creating a circular wait condition.

46. What are the four conditions for deadlock?

Answer: The four necessary conditions for deadlock (Coffman conditions):

1. Mutual Exclusion: Resources cannot be shared

2. Hold and Wait: Process holds resources while waiting for others

3. No Preemption: Resources cannot be forcibly taken

4. Circular Wait: Circular chain of processes waiting for resources

47. What are deadlock prevention techniques?

Answer: Deadlock prevention eliminates one of the four deadlock conditions:

• Mutual Exclusion: Make resources shareable (not always possible)

• Hold and Wait: Require processes to request all resources at once

• No Preemption: Allow resource preemption

• Circular Wait: Order resources and request them in sequence

48. What is the Banker's algorithm?

Answer: Banker's algorithm is a deadlock avoidance algorithm that checks if resource allocation will lead to a safe state. It simulates allocation and checks if all processes can complete.

49. What is a monitor in operating systems?

Answer: A monitor is a high-level synchronization construct that combines data, procedures, and synchronization in a single module. Only one process can be active inside a monitor at any time.

50. What is the producer-consumer problem?

Answer: The producer-consumer problem involves coordinating processes where producers generate data and consumers use it. It requires synchronization to prevent buffer overflow/underflow and race conditions.

File System Questions (Questions 51-55)

51. What is a file system?

Answer: A file system is a method of organizing and storing files on storage devices. It provides a logical structure for data storage and retrieval, managing file names, directories, and metadata.

52. What are the different file allocation methods?

Answer:

• Contiguous: Files occupy consecutive disk blocks

• Linked: File blocks linked using pointers

• Indexed: Index block contains pointers to file blocks

53. What is the difference between an absolute and a relative path?

Answer:

• Absolute Path: Complete path from root directory (e.g., /home/user/file.txt)

• Relative Path: Path relative to current directory (e.g., ../documents/file.txt)

54. What is fragmentation in file systems?

Answer:

• Internal Fragmentation: Unused space within allocated blocks

• External Fragmentation: Free space is scattered across the disk in small, unusable pieces

55. What are hard links and soft links?

Answer:

• Hard Link: Direct reference to file data, shares the same inode

• Soft Link (Symbolic Link): Pointer to another file path, has its own inode

Conclusion: Basic operating system interview questions

Mastering these 55 basic operating system interview questions will significantly boost your confidence and performance in technical interviews. Remember that understanding the concepts behind each answer is more important than memorizing responses word-for-word.

The key to success lies in being able to explain these concepts clearly and relate them to real-world scenarios. Practice explaining these answers out loud, and don't hesitate to ask follow-up questions or provide examples during your interview.

Good preparation in operating systems fundamentals demonstrates strong computer science foundations and problem-solving abilities that employers value highly. Use this guide as your roadmap, but continue exploring advanced topics as you grow in your career.

Key Takeaways

• Master Process Fundamentals: Understand processes, threads, PCB, and context switching thoroughly 

• Memory Management is Critical: Know virtual memory, paging, segmentation, and page replacement algorithms 

• CPU Scheduling Matters: Be familiar with FCFS, SJF, Round Robin, and Priority scheduling algorithms

• Synchronization is Essential: Understand race conditions, critical sections, semaphores, and deadlock concepts 

• File Systems Count: Know file allocation methods, directory structures, and path concepts 

• Practice Explaining: Be able to articulate concepts clearly with real-world examples 

• Understand Trade-offs: Know the advantages and disadvantages of different approaches 

• Real Interview Focus: These 55 questions represent the most commonly asked OS interview questions

• Conceptual Understanding: Focus on understanding rather than rote memorization 

• Connect Concepts: Show how different OS components interact with each other 

• Practical Application: Relate theoretical concepts to actual system behavior 

• Preparation Strategy: Use this guide systematically, covering each section thoroughly

Improve your software testing flow with advanced API testing tools

Talk to us today

Frequently Asked Questions (FAQs)

How many OS questions should I expect in a technical interview?

Most technical interviews include 5-10 operating system questions, focusing on fundamental concepts like process management, memory management, and CPU scheduling. Senior positions may include more advanced topics.

Should I memorize all these answers exactly?

No, focus on understanding the concepts rather than memorizing exact answers. Interviewers appreciate candidates who can explain concepts in their own words and provide relevant examples or analogies.

Which topics are most important for entry-level positions?

For entry-level positions, focus heavily on process management (questions 1-15), basic memory management (questions 16-25), and fundamental CPU scheduling (questions 31-35). These form the core of most basic OS interviews.

How do I handle questions I don't know completely?

Be honest about what you don't know, but explain what you do understand about the topic. Show your problem-solving approach and willingness to learn. Partial credit is often given for demonstrating thought processes.

Are coding questions common in OS interviews?

While most OS questions are conceptual, some interviews may include simple coding problems related to process synchronization, basic algorithms, or system calls. Focus primarily on concepts for basic OS interviews.

What's the best way to practice these questions?

Practice explaining answers out loud, create flashcards for key concepts, work through examples step-by-step, and try to connect different concepts together. Teaching others is also an excellent way to reinforce your understanding.

Should I study specific operating systems like Linux or Windows?

While understanding general OS concepts is most important, having some familiarity with Linux commands and concepts can be beneficial, as many companies use Unix-like systems. However, focus on universal OS principles first.

How detailed should my answers be during the actual interview?

Start with a concise answer covering the main points, then be prepared to dive deeper if the interviewer asks follow-up questions. Gauge the interviewer's reaction and adjust your level of detail accordingly.

Article Sources

1. GeeksforGeeks - Operating Systems Interview Questions 

2. InterviewBit - 40+ Operating System Interview Questions

3. JavaTpoint - Operating System Interview Questions 

4. PrepInsta - Top Operating System Interview Questions

5. TutorialsPoint - Operating System Interview Questions 

6. Unstop - Top 50 Operating System Interview Questions